As the pneumatic tire which can run on flat, in other words, the tire which, even when it is punctured, resulting in the tire internal pressure being dropped down to 0 kg/cm2, can run a certain distance safely (which is hereafter to be called the run-flat tire), the inner ring type tire in which an annular inner ring (support) made of metal or synthetic resin is mounted to the rim portion of the tire in the air chamber is known (referring to the patent literatures 1 and 2, for example).
As this inner ring type tire, the rotary inner ring type tire in which the inner ring is incorporated in the rim, and the dual-convex inner ring type tire in which the inner ring is mounted to the rim, having two convex parts in the tire radial direction section (referring to the patent literatures 3 to 6, for example) are known. The rotary inner ring type tire requires a special wheel to fix the rotary inner ring thereto, thus presenting a problem about versatility. On the other hand, the dual convex inner ring type tire is mounted to the conventional rim, thus offering a high versatility.
The ordinary vibration-proof rubber is used in the temperature range equivalent to that of the open air temperature, while the inside of the tire is at high pressure due to the pressurized air, and in addition, at the time of running, it has an increased temperature, thus the environment is presupposed to be significantly hard and easy to cause degradation. However, the conventional art has not sufficiently considered the degradation of the supporting part main body and the corrosion when the main body is made of metal.
The annular support is required to function only at the time of run-flat running, thus it is preferably made up of light-weight materials. When the car is run with such support being assembled in the tire, within which not only the moisture, but also the rubber-compound derived acidic ions, and the like, exist, and the temperature is raised, the possible degradation of the support resulting from it being kept inside the tire for a long term cannot be neglected, even if the tire is not punctured.
In addition, with the run-flat tire support, an annular leg part is bonded to both end parts of the supporting part thereof, and through the leg parts, the support is mounted to the rim. At this time, in order to improve the bondability between the respective end parts of the supporting part and the leg part, the bonding portion of the supporting part has been subjected to a surface roughening treatment by shot blasting in some cases.
However, with the above-mentioned surface roughening treatment, it has been impossible to maintain a high adhesive strength for many hours.
In addition, regardless of whether the above-mentioned surface roughening treatment has been given or not given, the non-uniformity in bonding, or the like, of the bonding portion of the supporting part has caused corrosion, and the like, or caused poor bonding, which, in some cases, has had an ill effect on the run-flat characteristics, including the running stability and the durability.
Further, in the portion of the supporting part to which the leg part is not bonded, the metal is exposed, thus there has been a problem about corrosion resistance, such as that rust may be produced, and the like.
At the time of run-flat running when the internal pressure for the tire has been lowered for some cause, the support as a complex of the supporting part made of metal and the rubber leg part bears the load, however, by this load, the complex is subjected to repetitive distortion while being rotated, and this distortion results in heat generation. The capability of run-flat running assures that the car can run a certain distance with no problems (for example, that it can run 50 km at a speed of 80 km/hr, and the like), however, the heating temperature of the supporting complex when the car has run this distance may exceed 150° C., depending upon the open air temperature. In such a case, with the support which has been formed by applying the conventional two-liquid coating type vulcanization bonding agent for parts jointing, peeling is caused at the boundary between the final coating bonding agent for the supporting part and the rubber composition of the rubber leg part, which has presented that the car cannot run on flat for a sufficient distance.
In addition, at the time of run-flat running, emergency running with the internal pressure being lowered is provided, however, in this case, the convex part of the supporting part is brought into contact with the tire tread part rear surface, carrying the load. However, at the time of emergency running with the vehicle weight being large and the load to be carried being high, the load imposed on the tire tread part is large, which finally may cause a failure in the tire tread part, leading to impossibility of running.
In the patent literature 4, an inner ring which has an added lubrication system for suppressing possible damage to the tread part rear surface is disclosed, however, about suppression of tread damage by adequately setting the sectional geometry of the supporting part, the above-mentioned conventional arts disclose no specific matters.    Patent literature 1: Japanese Patent Laid-Open Publication (JP-A) No. 2002-377519    Patent literature 2: Japanese Patent Laid-Open Publication (JP-A) No. 2001-519279    Patent literature 3: Japanese Patent Laid-Open Publication (JP-A) No. 10-297226/1998    Patent literature 4: Japanese Patent Laid-Open Publication (JP-A) No. 2001-163020    Patent literature 5: Japanese Patent Laid-Open Publication (JP-A) No. 2003-48410    Patent literature 6: U.S. Pat. No. 6,463,974 B1